Digital and Computed Radiography:

Acceptance Testing and Quality Control

Napapong Pongnapang, Ph.D.

Department of Radiological Technology

Faculty of Medical Technology

Mahidol University

Bangkok, Thailand

MAHIDOL UNIVERSITYWisdom of the Land

Content

Digital Radiography

◦ Photostimulable Phosphor (CR)

◦ Flat Panel Detectors (DR)

Acceptance Testing Guidelines

Setting up a Quality Control Program

Computed Radiography

Photostimulable Luminescence

X-Rays Flat Panel Detector

Flat Panel Detectors

Direct DR (DDR): Amorphous Selenium Detector – matrix of transistors, without photon conversion layer

Indirect DR (IDR): Amorphous Silicon TFT or CCD with CsI conversion layer

Flat Panel Detector Configurations

Indirect DR Direct DR

Acceptance Testing - Purpose

To ensure the machine acquired meets

detail specifications under the commercial

contract

To ensure clinical quality of the machine

for optimal patient safety and image

quality

To set up baseline values for Quality

Control (QC) purpose

Acceptance Testing - Process

• Get list of equipment package (inventory)

• Check standard acceptance testing procedures specific to each equipment– American Association of Physicist in Medicine

(AAPM)

– Institute of Physics and Engineering in Medicine (IPEM)

– Others Organizations provide standards (IAEA –soon)

• Get Test Tools– Phantoms

– Dosimeter

– Other measurement equipments

Acceptance Testing - Components

X-Ray Tube

◦ kVp, Timer

◦ Tube Leakage

◦ HVL, Linearity, reproducibility

CR Plate/Scanner

Detectors

Patient Dose

Acceptance Testing : X-Ray Machine

Use similar methods for general x-ray

machines

Concerned Points

◦ Don’t direct expose the detector with high

dose!

◦ Use Lead apron to block the detector

Acceptance Testing – CR Protocols

Acceptance Testing (AAPM)

Phosphor Plate Dark Noise

System Linearity, Auto-Ranging and Exposure ResponseReceptor Reproducibility, Density Uniformity & Artifact Analysis

Phosphor Plate/Cassette Throughput

Laser Beam Function

Spatial Resolution

Wire Mesh Test - Resolution Uniformity Across Receptor

Low Contrast Sensitivity/ Detectability

Distance Accuracy Measurements and Aspect Ratio TestAccuracy/Thoroughness of Erasure Cycle

CR Acceptance Test/QC Consideration

Image Acquisition

Electro-mechanical readout

Image processing

PACS/RIS interface

Image handling

Recommended Acceptance Tests

Physical inspection/inventory/PACS

interface

Image plate uniformity and dark noise

Signal response: Linearity and Slope

Signal response: Exposure calibration and

beam quality

Laser beam function

High contrast resolution

Recommended Acceptance Tests

Noise-Low contrast response

Distortion

Erasure thoroughness

Artifacts analysis

Positioning and collimation robustness

Image plate throughput

Acceptance Test Tools Required

Exposure / dose meters

Spatial resolution phantom

Low contrast phantom

SMPTE pattern

Anthropomorphic phantom

Document log/spreadsheet/instructions

Phosphor plate dark noise

The resultant film (or soft-copy image) for each plate should demonstrate a clear, uniform, artifact-free image.

Exposure indicators for automatic processing should indicate no incident exposure.

Obvious artifacts, density shading, or uniformities present on any output image should be evaluated further.

System Linearity, Auto-ranging and Exposure

Response

Make sure linearity response of CR

system

Test by calibrating 1 mR exposure at

specific vendor condition

Fuji use S = 200 Semi-Auto mode

exposed at 80 kVp @ specified distance

Other vendors; refer toTG10

It reflects the center of the usable portion of the

histogram

Calibration is based on a 1 mR exposure at 80 kVp

to the IP. Using a 72” distance through air to achieve

an “S” number of 200 with a fixed latitude of 1.

“S” Number - Sensitivity

Receptor Reproducibility, Density

Uniformity & Artifact Analysis

Make sure uniform image intensity across

irradiated field

At same exposure and image processing

condition, same uniformity is expected

No artifacts should be detected.

Phosphor Plate/Cassette Throughput

Make sure throughput meets with

vendor’s specifications

Fuji FCR 5000+ = 109 plates/hr

Spatial Resolution

Make sure spatial resolution meets

specification provided by vendors

This test requires same test conditions

specified by vendors

There are many factors affecting

resolution

Wire Mesh Test - Resolution Uniformity

Across Receptor

Similar to screen-film contact test done in

conventional radiography

To make sure uniformity across receptor

Wire Mesh Test - Resolution Uniformity

Across Receptor

Low Contrast Sensitivity/ Detectability

To test low contrast sensitivity of CR to

different levels of radiation dose

To see effects of SNR levels

Low Contrast – UAB Phantom

Low contrast at 5 mR

2.9%

Low contrast at 1 mR3.28%

Distance Accuracy Measurements and

Aspect Ratio Test

To test accuracy of distance measurement

Test by imaging a known size object

Distance Accuracy Measurements and

Aspect Ratio Test

Accuracy/Thoroughness of Erasure Cycle

Make sure that erasure cycle functions

well

Need very high radiation exposure and

dense material

Accuracy/Thoroughness of Erasure Cycle

BEFORE AFTER

Acceptance Testing – DR Protocols

Currently, no published dedicated

protocol available

IPEM No.91describes extended methods

to test Flat panel on top of general x-ray

equipment testing

AAPM is likely to release TG 151 in 1-2

years

DR Test Protocols

• What are now available?

– IPEM

–AAPM TG 116 – for Exposure Index Standards

–AAPM TG 18 – for Display Devices

–Vendor Specific Test Protocols

• GE

• Siemens

• Philips

• Cannon

• Others

Review: Available International/National

Standards

Deutsches Institut Fur Normung,

Germany

◦ DIN 6868-58 (2001) – Part 58

The Institute of Physics and Engineering in

Medicine, UK

◦ IPEM Report #91 (2005)

KCARE, UK

◦ Provides details on how to do acceptance

testing for DR

What are recommended?

• DIN 6868-58

– Dynamic Range

– Limited Spatial resolution

– Low Contrast

– Homogeneity

– Artifacts

• KCARE DR

– Dosimetry

– Dark Noise

– Detector dose indicator

consistency

– Uniformity

– Blurring and stitching artefacts

– Limiting spatial resolution

– Threshold Contrast at different dose levels

• IPEM

– Detector dose indicator monitoring

– Image uniformity

– Low contrast sensitivity

– Limiting spatial resolution

– Detector dose indicator reproducibility

– Measured uniformity

– Uniformity of resolution

– Threshold contrast detail detectability

– Scaling error

– Dark noise

Detector dose indicator monitoring

IPEM refers the method to the British

Institute of Radiology

Basicly, you check if the Detector Dose

Indicator corresponds to the dose

exposed to the detector

AAPM TG 116 provides details on

Exposure Index for different vendors

Exposure Index

www.philips.com

Exposure Index

www.philips.com

Image Uniformity

Expose blank

detector to see any

lines or rectangular

areas

If any seen, detector

needs to be

recalibrated

Low contrast sensitivity

Test contrast level at different dose to

detector

Needs test objects such as Leeds TOR

and Cu attenuator (or equivalent)

Establish baseline for future comparison

Low Contrast – UAB Phantom

Low contrast at 5 mR

2.9%

Low contrast at 1 mR3.28%

Limiting Spatial Resolution

Lead grating resolution bar pattern is

recommended

Use low tube voltage about 50 kVp

without filtration

Angle the test pattern at 45 degree

Establish baseline for future comparison

Line pairs test pattern

Detector dose indicator repeatability

Expose the detector with same dose for

3 times

Record the Exposure Index

70 kVp with 1.0 mm Cu attenuator is

recommended for dose of 10 uGy

Detector dose indicator reproducibility

Similar to previous test but do at different

dose levels

Can be used as monitoring tool for long

term decline of the system

Measured Uniformity

Use image from previous test

Draw 5 ROIs about 100x100 pixels

Calculate SD from five ROIs divide by the

mean value

Uniformity of resolution

Use fine wire mesh

Expose at low tube

potential at 50 kVp,

SID = 1 meter

No filtration added

Check for blurred

areas

Scaling Error

Use highly attenuated objects such as

ruler or test pattern with grids of known

distance

Check for accuracy of distance

measurement

Repeat with film, if laser printer is used.

Dark Noise

Obtain image with no or very low

exposure

Purpose is to check electronic noise

Can also expose the detector using highly

radiation attenuated block

Setting up a QC Program for DR

Quality Control

Modern equipments have good maintenance

program, why need QC?

QC = maintain standard

◦ For image quality, dose and safety

Results of QC can be used to dictate level of

action

◦ For further tests needed, call engineer, stop scanning

◦ Reassurance of ongoing quality, solving clinical image

problems, provide evidence to manufacturer

How do we get start?

Medical physicist performs acceptance testing

Medical physicist sets up QC activities run by

QC Technologist/Physicist

IPEM Recommendation:

Routine Testing for DR

What is needed?

Computer friendly phantom

Objective quantitative analysis method

System performance tracking and

database logs

Exposure monitoring tools and database

tracking

CR/DR QC Phantom

CR/DR EZ - Daily QC PhantomOne shot image quality evaluation

CR/DR QC Phantom

ACR R/F Accreditation Phantom

Daily QC

Hard copy/Display QC

SMPTE/TG-18 Test Pattern

Laser Film QC

Weekly:

View SMPTE pattern

Verify gray levels

• 0/5% & 95/100%

patches

Film 6 on 1

• 4 on 1 if necessary

Plot OD of

• 10%, 40% & 90&

patches

Observe film for

artifacts

SMPTE Test Pattern

Action Limits

SMPTE

patch

OD Control

Limit

0 2.45 0.15

10% 2.10 0.15

40% 1.15 0.15

90% 0.30 0.08

Conclusion

Digital Radiography includes PSP, IDR and

DDR

Acceptance Testing and QC for each type

of the technology are different

Numbers of standard test protocols are

available but not harmonized

Acceptance test procedures and set up

QC program must be done to ensure the

quality of the radiological services

provided